Electric arc lamp



Nov. 16, 1937. w. c. MITCHELL 2,099,073

ELECTRIC ARC LAMP Filed March 15, 1935 Tic. 1

ATTORNEY.

Patented Nov. 16, 1937 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates generally to improvements in electric arc lampsof the enclosed bulb or tube type, and specifically to means forpreheating electrodes, ionizing gaseous substances 5 therebetween andautomatically adjusting the arcing gap in accordance with the mostefiicient starting and operating requirements.

It is a principal object of my said invention to provide an incandescentbulb lamp, preferably of common and well known form, in which,principally for the production of the ultra-violet rays for therapeuticpurposes, an electric arc may be formed and maintained, and which isadapted for use in the standard incandescent lamp socket 15 and inconnection with the usual lighting circuit.

A common form of electric mercury-vapor arc lamp in extensive use forthe purpose mentioned, is known by the trade-name Sunlamp, manufacturedand distributed by the General Electric Company. Not being designed foruse with standard incandescent lighting fixtures, and requiring atransformer to cut down the usual lighting circuit voltage, the Sunlampcan only be employed with specially designed fixtures, including atransformer built in the base of the supporting holder or stand.

It is an important object of the present contribution to the art toeliminate the transformer, and by such design as will permit use in thestandard incandescent lamp socket to avoid the necessity of speciallyconstructed fixtures and supports, thus saving expense.

Still another object is the provision in an arc lamp of adequate meansfor most eificiently pre- 35 heating electrodes and. ionizing gaseoussubstances between them for the initial formation of the arc, and theprovision of thermostatic means by which, when formed, the arc isautomatically adjusted as to length for the best ray- 40 producingresults.

Efiiciency, particularly as it relates to the production of maximumultra-violet radiations by the proper automatic spacing of the arcingpoints, simplicity, and consequent durability, re-

45 sulting both in economy of manufacture and of maintenance, are othervital objects of said invention.

Other objects and corresponding advantages will be apparent to those ofskill in the art from 50 the following detailed description.

In the drawing, Fig. 1 illustrates a combined prospective anddiagrammatic view of a prefered embodiment of my invention;

Fig. 2 is a similar view of a modification of 5 the same;

Fig. 3 is a like illustration of a second modified form.

Referring to the drawing in detail, the numerals of which indicatesimilar parts throughout the several views, 5 designates a glass bulbsubstantially exhausted of air, mounted in a base, '6, of conventionalform. In the bottom of bulb 5 a drop of mercury 1, adapted to bevaporized by means about to be described, is placed.

Lead wires, 8 and 9, from the usual terminals are held rigidly in aglass neck In, which is secured in the base 6, in a manner well known inthe art. Filament II connects the ends of wires 8 and 9, said latterwire being longer and having a curved extension, 9a, at its end, permitsfilament H to be obliquely disposed relative thereto. Secured to wire 9adjacent glass neck I0 is a thermostatic conductor l2, of laminatedcomposite construction, comprisingtwo strips of metal of differentrelative thermic expansibility, adapted to be heated by theincandescence of filament H, and arranged so as, after the formation ofthe arc, to bend away under the influence of heat, from wire 8, ashereinafter more fully explained.

l3 indicates an electrode preferably composed of tungsten, secured towire 8 proximate its lower end, adapted in operation to form an arcingpoint with a second similar electrode M on the end of thermostat l2,both of which electrodes are located directly above filament H and de-'signed so that there is only a small gap between them when cold.

In operation of the lamp an electric circuit is established through wire8, filament H and wire 9, which immediately incandesces said filament inthe manner and for reasons well known in the art. The heat generated bythe incandescence of filament l l radiates to the electrodes, heatingthem and also vaporizing the mercury located in the bottom of the bulb5, thus producing necessary ionization to facilitate the formation of anare between the electrodes. There being less resistance through theelectrodes, once heated and the are started the electric current throughfilament II ceases, and the current continues to maintain the arc.

The heat generated by the arc affects the thermostatic conductor l2which bends away from wire 8, widening the gap between the electrodesand regulating the length of the arc. The electrode M will return to itsinitial position when cooled due to the different ratio of contractionof the elements comprising the thermostat.

It is thought that the general principles and mode of operation fullyexplained, the different forms in which my invention may be utilized asexemplified, for instance,-in Figs. 2 and 3 of the drawing, will bequite clear to all of skill in this art, and that further details ofdifferentiation between such illustrations need not be set forth.

It will be understood that I do not limit myself to any particular formor material of bulb or tube, nor to kind or character of materials ofconductors, electrodes or their arcing points; neither do I limit myinvention to any of the specific forms of filaments nor their relativearrangements with respect to the thermostatic element as illustrated inthe different figures of the drawing, as it will be obvious that suchinvention may be embodied in other forms and arrangements with likeefi'ects.

It will be apparent that I have produced a device in which the greatinitial heat of the filament necessary to vaporize the mercury and heatthe electrodes, which, if continued, would be destructive to the lamp,will, with proper design by those of skill in this art, be extremelybrief, and the necessity of employing what is known as thepoor-regulation transformer in which an initial high voltage is quicklycut down to avoid destructive efiects is eliminated. When formed, thethermostatic member being properly designed, the arcing electrodes willbe gradually separated to maximum space, permitting efiicient operation.

What I claim and desire to secure by Letters Patent is:

' 1. In an electric arc lamp, a pair of terminals, a lead wire connectedto each of said terminals, a resistance coil rigidly secured at oppositeends to said wires so as to form and maintain a conductor from one ofsaid wires to the other thereof, an electrode connected to one of saidwires, a movable electrode connected to the other of said wires by abi-metal thermostat, said thermostat normally spacing said movableelectrode from said first-mentioned electrode and adapted to furtherseparate said electrodes when heated by the formation of an arctherebetween, and a substance adapted to be ionized by the heat of saidresistance coil to form and maintain during all stages of relativemovement of said electrode a conductor between said electrodes of lessresistance than said resistance coil.

2- In an electric arc lamp, a pair of terminals, a sealed bulb, a leadwire connected to each of said terminals extending into said bulb, aresistance coil rigidly secured to opposite ends of said wires so as toform and maintain a conductor from one of said wires to the otherthereof, an electrode connected to one of said wires, a movableelectrode connected to the other of said wires by a bi-metal thermostat,said thermostat normally spacing said movable electrode from saidfirst-mentioned electrode and adapted to further separate saidelectrodes when heated by the formation of an arc therebetween, and asubstance within said bulb adapted to be ionized by heating, saidresistance coil being adapted upon the passage of an electric currenttherethrough to simultaneously ionize said substance and heat saidelectrodes to provide and maintain a conductor across said electrodesduring all stages of relative movement thereof of less resistance thanthat of said resistance coil.

3. In an electric arc lamp, a sealed bulb, a pair of terminals, a leadwire connected to each of said terminals extending into said bulb, saidlead wires having their opposite ends inseparably connected by means ofa resistance filament, an electrode carried by one of said lead wires, abimetal thermostat supporting a second electrode adjacent thefirst-mentioned electrode but adapted to maintain a gap therebetween,having its opposite end connected to the other of said wires so as toform an electricity-conductive by-pass around and of less resistancethan said resistance filament upon the formation of an are between saidelectrodes, said thermostat being adapted to increase the gap betweensaid electrodes upon being heated by said arc, embodying means to limitthe separation of the electrodes and thereby limit the resistance tosaid are caused by such separation to a point below the resistance ofsaid resistance filament, and means within said bulb adapted to beionized by heat from said resistance filament to form a conductorbetween said electrodes.

4. In an electric arc lamp, a pair of terminals, lead wires from saidterminals into a sealed bulb, an electrode connected to one of said leadwires, a second movable electrode connected to the other of said leadwires by means of a bi-metal thermostat, said thermostat being adaptedto maintain a gap between said electrodes, a substance adapted to beionized by heat to permit the formation of an are between saidelectrodes, and a resistance coil inseparably connecting said lead wiresof greater resistance to the flow of electricity than the electrodes andthe area therebetween.

5. In an electric arc lamp, a pair of terminals, means comprising a pairof lead wires and a resistance heater-coil to connect said terminals andinseparably maintain a conductor therebetween, an electrode secured toone of said lead wires, a second electrode, a thermostat connected tothe other of said lead wires to support said second electrode in aposition spaced from said first electrode, said resistance heater-coilto ionize the gas between said electrodes, said thermostat beingsubstantially unaffected by'the heat of said heater-coil but movable bythe heat of said are to further separate said electrodes, saidresistance heater-coil forming an electricity-,

conductive circuit between said lead wires of greater resistance thanacross said electrodes.

6. In an electric arc lamp, a pair of terminals, means comprising a pairof lead wires and a resistance heater-coil to connect said terminals andinseparably maintain a conductor therebetween, an electrode secured toone of said lead wires, a second electrode, means connected to the otherof said lead wires to support said second electrode in a position spacedfrom said first electrode, said resistance heater-coil to ionize the gasbetween said electrodes whereby an arc will form between saidelectrodes, said resistance heater-coil forming anelectricity-conductive circuit between said lead wires of greaterresistance than across said electrodes.

WALTER C. MITCHELL.

